The present invention relates to substantially omnidirectional antennas, particularly a stacked biconical antenna.
The present invention relates to substantially omnidirectional antennas, particularly stacked biconical antennas.
Biconical antennas have commonly been used for their omnidirectional characteristics in azimuth. It has been discovered that for any given desired gain, the volume for a biconical antenna can be reduced by replacing a single biconical with a stacked array of a plurality of biconical antenna elements. Several examples of stacked biconical antennas are discussed below.
U.S. Pat. No. 3,159,838 (Facchine) discloses a single biconical antenna with a coaxial feed cable. This and all other patents cited herein are hereby specifically incorporated herein by reference in their entirety. Attached to the feed cable are smaller cables that bring electromagnetic energy to the biconical antenna. The feed point is close to the main cable since otherwise there may be interference from the smaller feed cable.
U.S. Pat. No. 5,534,880 (Button) discloses a stack of biconical antennas in which a radome supports the structure of the antenna. A transmission wire bundle is helically spiraled within the radome to provide electromagnetic energy to the biconical antenna elements. Separate transmission wires emanate from the main transmission wire bundle and connect directly to the radiating elements to provide energy to each biconical antenna element.
The shortcomings of the prior art are twofold. First, the wiring required to provide energy to the antenna induces interference with the outgoing signal, distorts the omnidirectional radiation pattern, induces interference with the incoming signal, and requires the use of a power divider. Second, the structure of some of the antennas necessitates a radome to support the structure of the antenna. It has also been found that the simpler mechanical design of the present invention leads to an antenna with a more rugged and robust performance.
The present invention is directed to a substantially omnidirectional antenna comprising a plurality of stacked biconical antenna elements, wherein each of the biconical antenna elements is formed by a two truncated flared apart conductive cones with a bore perpendicular to the base of each cones. The antenna also comprises a plurality of nonconductive collars between adjacent cones. Further the antenna comprises a single feed line which passes through the biconical antenna elements and the nonconductive collars. The feed is in one of many possible configurations. One advantage of the device is its flexibility in that the feed""s characteristics determines the amount of energy released by each particular biconical antenna element. The antenna also allows the energy to be controlled and balanced in order to transmit a substantially uniform signal. Further, other parameters of the device also may be manipulated to change the amount of energy released by each biconical antenna element. Another advantage of the device is that the inner conductor is not in contact with the biconical antenna elements, allowing for a simpler mechanical design. In another embodiment, the substantially omnidirectional antenna of the present invention advantageously provides a gain of 8-10 dB that is maintained nearly identically over the entire 360 degree azimuth range.
The present invention is also directed to a method for sending a substantially omnidirectional wireless communication signal via an antenna. The communication signal is created by passing a feed line through the center of a plurality of biconical antenna elements and sending electromagnetic current through the feed line.
The present invention is also directed to a feed line for a substantially omnidirectional biconical array antenna. The feed line may be a tapered serial coaxial cable engineered to deliver the required energy to each element of the antenna. The feed line may also be a parallel coaxial cable engineered to deliver the required energy to each element of the antenna.
The present invention is also directed to a method of connecting an array of biconical antenna elements. The antenna is connected by stacking a plurality of biconical antenna elements, placing a nonconductive collar within each biconical antenna element, passing a rigid structure through the center of said biconical antenna elements and collars, and securing structure together by squeezing said biconical antenna elements and said nonconductive collars.